Angular channel-shaped coil insulation



June v15, 1965 L. 1-; FEATHER 3,189,681 ANGULAR CHANNEL-SHAPED COILINSULATION Fj led March 11, 1960 Fig. I

40 42 m l/4V] F lg. 5

INVENTOR Londis E. Feather ATTORNEY United States Patent 3,189,631ANGULAR CHANNEL-SIMPED CGIL INSULATIQN Landis E. Feather, HickoryTownship, Mercer County, Pa., assignor to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation of Penusyivania FiledMar. 11, 1960, Ser. No. 14,397 3 Claims. (Cl. 174-421} This inventionrelates to insulation for electrical apparatus, and particularly toinsulating barriers associated with multiple coil transformer windingswhich utilize nested barriers of insulating material.

In electrical apparatus, such as transformers, a large quantity ofbuilt-up pressboard spacing and insulating structures of a great varietyof dimensions and shapes is required. Such built-up structures areparticularly useful for insulating the live portions of transformersfrom the casing and for separating the electrical elements from oneanother.

Included among these insulating members for transformers and likeelectrical apparatus are angled channel members that are used toinsulate the inside corners and the outside corners of substantiallyrectangular coils, and particularly the rectangular coils in pancakeform used in shell-type transformers.

Heretofore, in preparing insulating structures for rectangular coils,and particularly the angled channel members, a special grade ofpressboard or fuller board was first soaked in water and worked by handinto a condition such that a cold-pressed preform could be preparedtherefrom. After the preform was dried, it was then moistened andinserted into a suitably formed mold and hot pressed to form the desiredstructure.

This invention is directed to electrically insulating channel membersadapted for use as insulating barriers for the windings of transformercoils, particularly the rectangular coils in pancake form. Theinsulating channel members of this invention comprise a pair of sidewalls depending from an end wall, the side walls and end walls formingsubstantially continuous U-shaped channels. The U-shaped channel will bedisposed at certain angles depending upon the configuration of the coilto which the insulating channel member is applied. The channeledinsulating members of this invention are laminated members formed from aplurality of plies of a specific stretchable paper sheet material and aspecific thermoplastic bonding resin.

For a complete understanding of the nature of this invention, referenceis made to the following detailed description taken in conjunction withthe drawing, in which:

FIG. 1 is a front elevational view of a stack of resintreated sheetmaterial prior to molding;

FIG. 2 is a view in perspective of a channel member of this invention;

FIG. 3 is a View in perspective of another channel member of thisinvention;

FIG. 4 is a plan view of a transformer coil of the pan cake type showingan inside angled channel member applied thereto; and

FIG. 5 is a cross-sectional view taken on the line V-V of FIG. 3.

In accordance with this invention, it has been determined that highlysatisfactory channel members adapted for barrier insulation for coilssuch, for example, as rectangular pancake coils used in the shell-typepower transformers, can be prepared by molding in a suitable mold withthe application of heat and pressure a plurality of plies of a specificcreped paper treated with a specific thermoplastic resin adhesive.

The specific crepe paper employed in preparing the accompanyinglaminated channel members of this invention is a crepe paper prepared bycreping a high density sulfate kraft paper. The sulfate kraft paper,prior to creping, has a basis weight of from about 70 pounds to 85pounds, and a thickness of about 5 mils. The high density sulfate kraftpaper is creped in the machine direction by known methods to provide asheet of creped paper having a thickness of from about 40 mils to 50mils and a stretch of at least about 200% in the machine direction. Thepaper has from about 30 to 40 crimps per inch.

The thermoplastic resinous adhesive or bonding material employed to bondtogether a plurality of plies of the above-described crepe paper is apolyvinyl acetate resin.

The degree of polymerization of vinyl acetate can be controlled bymethods known in the art to produce polyvinyl acetates of variousdegrees of polymerization. Polyvinyl acetates that have given verysatisfactory results in this invention are the polyvinyl acetates, asolids solution of which in acetone at C. will have a viscosity of fromabout 15 to seconds as measured by a No. 4 Ford cup whose use isdescribed in Protective and Decorative Coatings, by Mattiello, volume 5,page 187,

1946 edition.

The polyvinyl acetate is applied to the creped paper in solution form,usually of about 50% solids content. Suitable solvents for polyvinylacetates are known in the art and include toluene, methanol, ethanol,methyl ethyl ketone, acetone, and mixtures of two or more.

The polyvinyl acetate is applied to the crepe paper in any convenientmanner as, for example, by passing the paper through a varnish dip pancontaining a solution of the polyvinyl acetate in toluene andsubsequently evaporating from the treated crepe paper the toluenesolvent by the application of external heat.

The sheet of creped paper is treated to a resin ratio of from about 1.10to 1.20. Resin ratio is defined as the weight of the sheet plus theweight of the resin to the weight of the untreated sheet. Therefore, thetreated sheet of creped paper comprises polyvinyl acetate resin appliedthereto in an amount of from about 10% to 20% of the weight of the sheetalone.

Referring to FIG. 1 of the drawing, there is shown a stack 10 ofpolyvinyl acetate-treated creped paper. For the purposes of thisinvention, the stack 10 preferably comprises a top sheet 12 and a bottomsheet 14 of substantially the same length and width, while sandwichedtherebetween is a plurality of sheets 16 arranged in a pyramidal form asshown. The sheets 16 are of substantially the same width as sheets 12and 14 but are of varying lengths as shown. The sheets can be all of thesame size if desired. The preferred arrangement as shown in FIG. 1provides for relatively thin and flexible end portions on the channeledmembers prepared therefrom. The flexible and thin end portions providefor ease in nesting together the channel members when a plurality ofchannel members are applied to a coil member.

The stack 10 is placed in a suitable mold where it is formed by foldingand stretching the stack, and subjected to pressure of from about 250 to500 pounds per square inch and at a temperature of from about C. to C.for a period of time of from about 4 minutes to 6 minutes to produce anangled channel member 20 as shown in FIG. 2 of the drawing.

The channeled angle member 20 of FIG. 2 is adapted for use on the insidecorners of pancake coils and comprises side walls 22 and 24 dependingfrom a bottom wall 26. The side walls 22 and 24 and bottom wall 26 forma continuous substantially U-shaped channel in the member and the bottom26 of the channel formed thereby is curved substantially at a rightangle. End portions 21 and 23 of the member 2% are tapered andrelatively thin owing to the arrangement of the sheets of stack ill asabove described. The thin flexible end portions 21 and 23 provide forease of nesting adjacent channel members. The laminated angled channeledmember 29 is fitted over one of the inside corners of a wound coil bodyto insulate the inside corners of the wound coil body from otherelectrical conducting members that comprise the electrical apparatus.

FIG. 3 of the drawing shows an angled channel member 3d of thisinvention adapted to be fitted over the outside corners of a wound coilbody. Channel member 3t) comprises side walls 32 and34 and bottom wall36.

As illustrated in FIG. 4 of the drawing, there is shown an angledchannel insulating member of this invention fitted over a Wound coilbody 42 of pancake form. The coil body 42 is formed of flat wound copperstrap with some form of flat insulation (not shown) disposed between thelayers of copper strap. The coil body 42 is substantially rectangular inshape with a central opening therethrough for accommodating a magneticcore (not shown). As shown in FIG. 4, there is just one channeled angledmember 4% applied thereto; however, each of the inside corner anglesthereof will be provided with an angled channeled insulating member toprovide for insulating the wound coil body 42 from a magnetic core whichwill be subsequently placed Within the central opening therethrough. Theoutside corner angles of coil body 42 can be insulated with channelmembers formed as shown in FIG. 3 of the drawing. V

The laminated molded channeled angled members of this invention areeasily and readily prepared, and the stretch of at least 200% providedby the creped paper employedin preparing these members permits ofmolding of members of complex shapes, as for example, the angled channelmembers 2t and fill of FIGS. 2 and 3 of the drawing. Owing to the greatamount of stretch of the creped paper employed in carrying out thisinvention, members and can be formed by folding and stretching theplurality of plies of resin treated creped kraft paper so that theU-shaped channel provided therein is at an angle of about 90. However,members can also be prepared in which the U-shaped channel therein isbent at an angle of from about to 130. Heat and pressure aresubsequently applied to form a unitary structure. in practice theplurality of plies of resin treated creped paper are placed in a heatedmold where the'forming and stretching are accomplished in one operation.Pressure is applied during this operation to bond the plies togetherinto a unitary member of desired shape.

The laminated insulating angled channel members of this invention haveoutstanding electrical insulating properties and good mechanicalproperties. Furthermore, by preparing the members as above described,the members have excellent flexibility properties so that they can beeasily and readily applied to the Wound coil body.

While this invention has been directed specifically to laminated angledchannel members for insulating inside corner angles of coil bodies such,for example, as coil bodies of pancake form, it will be understood thatother insulating bodies of complex structures and shapes can be easilyand readily prepared therefrom.

It is'to be understood that the above description and drawing areillustrative of the invention, and not in limitation thereof,

I claim as my invention:

1. An insulated electrical coil comprising, in combination, anelectrical conductor having curved surfaces and a flexible insulatingchannel member applied to at least one of the curved surfaces thereof,said channel member comprising a plurality of plies of high densitycreped kraft paper sheeting having about 36 to 40 crimps per inch, eachof said plies having an original thickness of from about 40 mils to 50mils and a stretch of at least about 200% and-a polyvinyl acetate resinbonding the plurality of plies of creped kraft paper into a unitarymember, said member having side walls and a bottom wall forming achannel conforming to the configuration of the curved surface of theelectrical conductor and fitting snugly over the surfaces thereof, andsaid crimps in each ply disposed essentially laterally with respect tosaid bottom wall.

2. insulated electrical coil comprising, in combination, an electricalconductor having curved surfaces and a flexible insulating channelmember applied to at least one ofthe curved surfaces thereof, saidchannel member comprising a plurality of plies of high density crepedkraft paper sheeting having about 30 to 40 crimps per inch, each of saidplies having an original thickness of from about 41) mils to 50 mils anda stretch of at least 200% and a resin bonding the plurality of plies ofcreped paper into a unitary member, said resin consisting of a polyvinylacetate resin, said polyvinyl acetate resin being present in an amountof from about 16% to 28% by weight of the'sheet material alone, saidflexible insulating channel member having side walls and a bottom wallforming a channel conforming to the configuration of a curved surface ofthe electrical conductor and fitting snugly over the surface thereof,and said crimps in each ply'disposed essentially laterally with respectto said bottom'wall.

3. An angular channebshaped electrically insulating memberconsistingessentially of a plurality of plies of high density creped kraft papersheeting having about 30 to '40 crimps per inch, each of said plieshaving an original thickness of from about 40 mils to about 50 mils anda stretch of at least 200%, a polyvinyl acetate resin bonding the pliesof creped paper into a unitary member, said member having side wallsdepending from a bottom Wall thereby defining a U-shaped channel, saidbottom wall curved. to define an angle of about 40 to about and saidcrimps in each ply disposed essentially laterally with respect to saidbottom wall.

Reierences Cited by the Examiner UNITED STATES PATENTS 1,488,504 4/24Keyes l56222 X 1,735,684 11/29 lurgensen 156-222 2,025,540 12/35 Langleyl56190 2,135,315 11/38 Walters et al. 336-209 2,576,864 ll/5l Valente156-222 X 2,749,525 6/56 Henderson 336-209 2,754,355 7/56 Bartlett336-206 X FOREIGN PATENTS 577,676 5/46 Great Britain. 466,975 a 8/50Canada.

JOHN F. BURNS, Primary Examiner;

MILTON 0. l-llRSl-iFlELD, C. F. .(RAFET,

LARAMEE E. ASE-ZEN, E. IAMES SA), examiners,

3. AN ANGULAR CHANNEL-SHAPED ELECTRICALLY INSULATING MEMBER CONSISTINGESSENTIALLY OF A PLURALITY OF PLIES OF HIGH DENSITY CREPED KRAFT PAPERSHEETING HAVING ABOUT 30 TO 40 CRIMPS PER INCH, EACH OF SAID PILESHAVING AN ORIGINAL THICKNESS OF FROM ABOUT 40 MILS TO ABOUT 50 MILS ANDA STRETCH OF AT LEAST 200%, A POLYVINYL ACETATE RESIN BONDING THE PLIESOF CREPED PAPER INTO A UNITARY MEMBER, SAID MEMBER HAVING SIDE WALLSDEPENDING FROM A BOTTOM WALL THEREBY DEFINING A U-SHAPED CHANNEL, SAIDBOTTOM WALL CURVED TO DEFINE AN ANGLE OF ABOUT 40* TO ABOUT 130*, ANDSAID CRIMPS IN EACH PLY DISPOSED ESSENTIALLY LATERALLY WITH RESPECT TOSAID BOTTOM WALL.